Compact fluorescent lamps typically comprise a lamp tube with a number of 180.degree. convolutions, or bends, to achieve compactness, while maintaining a long tube length. Located at each end of the lamp tube is a respective pair of elongated conductors connected across the ends of a filament-heated type of cathode within the lamp tube. Such conductors are referred to herein as cathodes, or elongated cathodes. The cathodes are connected to ballast circuitry to suitably condition the current supplied to the cathodes. The ballast circuitry, in turn, is typically connected to an Edison-type screw base for installation into a conventional incandescent lamp socket. A first aspect, or feature, of the present invention relates in particular to the lamp cathode-to-ballast connection.
One prior art practice of connecting lamp cathodes to ballast circuitry has been to make such connection using so-called wire crimps. Thus, the end of a cathode is placed in one end of a wire crimp (i.e., a cylindrically shaped conductive member), and a wire from the ballast circuitry is placed in the other end of the wire crimp. The wire crimp is then compressed to make a mechanically and electrically sound connection between cathode and ballast circuitry. The installation of a wire crimp, however, has been carried out with manual labor. Especially due to the small dimensions involved, the use of wire crimp is a difficult and, hence, expensive procedure.
Concerning a second aspect (or feature) of the invention, a trend in the design of compact fluorescent lamps has been to increase lamp wattage, to achieve higher light output. Such lamps include an envelope, or tube, in which suitable fill materials are provided to produce light. The cathodes of the lamps are of the filament-heated type, and are maintained at a high temperature to assure proper lamp operation. With the ballast circuitry for the lamp positioned adjacent lamp tube and heated lamp cathodes, the increased heat from the increased-wattage lamps causes ballast temperature to increase. It is known that for every 10 degrees Celsius increase in temperature, the wear out of various ballast components (e.g., electrolytic capacitors) is accelerated by about 50 percent. Other factors increase ballast temperature, such as placing ballast circuitry within a recessed fixture that limits ballast cooling, or including an amalgam in the fill of the lamp tube which results in system temperature increase in certain application (e.g., in a recessed lamp fixture).
As detailed below, the present inventors performed a considerable number of thermal studies on compact fluorescent lamps to determine a simple (e.g., low cost) and effective approach to limiting ballast temperature.